Recently, fiber Bragg gratings (FBGs), as a novel and robust sensor, has already been successfully applied to measure the internal early age shrinkage and the temperature changes in ordinary Portland cement. Currently, magnesium phosphate cement is becoming a popular material for structure repair and reinforcement as its fast setting properties. In this paper, the basic material is actually magnesium phosphate cement (MPC) mortar, with big difference from ordinary Portland cement. In spite of the existing discrepancy in the sample preparation, the fundamental sensing principles are same for OPC and MPC. After several sets of experiments we have been able to reach some initial inferences of physical properties of the composites from the patterns of changes of the strain during the solidification.